Alright. Very weird indeed.
Code:
<vb:if condition="$post['signature']">
<blockquote class="signature restore"><div class="signaturecontainer">{vb:raw post.signature}</div></blockquote>
{vb:raw template_hook.postbit_signature_end}
</vb:if>
{vb:raw template_hook.postbit_signature_end}
Somehow, I have two of those hooks in my postbit_legacy template.
Downloaded the 4.0 PL1 Forum, and the Suite, and the Style XML also have two signature_end hooks. Not sure if this is a bug in 4.0 PL1, but I posted it on the VB.com Bug Tracker.